Field of the Invention
The invention relates to a pyrolysis plant for refuse and a method for screening solid residues, through the use of which coarse solid fragments are separated from finer solid fragments.
In many industrial areas of use, it is necessary for solids which are contained, for example, in bulk material to be separated into a plurality of fractions. The fractions are, as a rule, subdivided according to different solid sizes, solid geometries or solid constitutions. Separation of solids is desirable whenever the different solid fractions are to be supplied for further treatment.
In the building industry, for example, building debris which occurs is separated from large and bulky debris constituents which are then sorted and reutilized. The separated finer building debris is disposed of, for example, at a dump provided for that purpose.
In the field of waste disposal, separation and sorting of the waste or of residues occurring during waste utilization are of ever-increasing importance with a view toward disposal which is as protective of the environment as possible. An essential factor therein is the separation of waste according to its size. Separation may be carried out before the waste is utilized. However, it may also be an essential method step in waste utilization itself.
Thermal methods are known for the elimination of waste, in which the waste is burned in refuse incineration plants or pyrolysed in pyrolysis plants, that is to say subjected to a temperature of about 400xc2x0 C. to 700xc2x0 C., with air being excluded. In both methods, it is expedient to separate the residue remaining after incineration or after pyrolysis, in order to either supply it for reutilization or dispose of it in a suitable way. The aim, in that case, is to keep the amount of residue to be ultimately stored at a dump as low as possible.
European Patent Application 0 302 310 A1, corresponding to U.S. Pat. No. 4,878,440, and a company publication entitled xe2x80x9cDie Schwel-Brenn-Anlage, eine Verfahrensbeschreibungxe2x80x9d [xe2x80x9cThe Low-Temperature Carbonization Incineration Plant, a Method Descriptionxe2x80x9d], published by Siemens AG, Berlin and Munich, 1996, disclose, as a pyrolysis plant, a so-called low-temperature carbonization incineration plant, in which essentially a two-stage method is carried out. In the first stage, the waste supplied is introduced into a low-temperature carbonization drum (pyrolysis reactor) and is carbonized there at low temperature (pyrolysed). During pyrolysis, low-temperature carbonization gas and pyrolysis residue occur in the low-temperature carbonization drum. The low-temperature carbonization gas is burned, together with combustible parts of the pyrolysis residue, in a high-temperature combustion chamber at temperatures of approximately 1200xc2x0 C. The waste gases occurring at the same time are subsequently purified.
The pyrolysis residue also has non-combustible constituents in addition to the combustible parts. The non-combustible constituents are composed essentially of an inert fraction, such as glass, stones or ceramic, and of a metal fraction. The useful materials of the residue are sorted out and supplied for reutilization. It is necessary to have methods and components which ensure reliable and continuous operation for the sorting-out process.
In the case of screening devices, there is often the problem of screen surfaces becoming clogged. The screening device then breaks down, or at least it must be subjected to complicated and labor-intensive cleaning. The problem of the blockage of the screening device arises particularly when the solid to be separated has a highly inhomogeneous composition. Thus, for example, wires catch in perforated plates used as screen surfaces, so that the individual holes are first narrowed and, in time, become clogged.
The residue occurring during the pyrolysis is typically a highly inhomogeneous solid which has pronounced differences in terms of its material composition, its size and the geometry of its solid fragments. The residue contains not only stones, broken glass and larger metal fragments, but also elongate bars and entangled wires (wire pellets).
A device for discharging pyrolysis residue from a low-temperature carbonization drum is known, for example, from International Publication No. WO 97/26495, in order to provide for the separation of coarse pyrolysis residue. The discharge device includes a conveying device which has a separating bottom with a sawtooth-like profile as well as a downstream bar screen. The separating bottom is set in vibration, so that the fine constituents are separated from the coarse on the separating bottom. The fine constituents fall through the downstream bar screen, while the coarse constituents slide along on the latter. However, wire pellets may catch on the bars and lead to a blockage.
It is accordingly an object of the invention to provide a pyrolysis plant for refuse and a method for screening solid residues, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which continuous operation is ensured by simple measures, without blockages occurring.
With the foregoing and other objects in view there is provided, in accordance with the invention, a pyrolysis plant for refuse, comprising a screening device having an interior for receiving solid residues, a rod wound along a helical line and bounding the interior, and a longitudinal axis, the screening device rotatable about the longitudinal axis.
The decisive advantage of a screening device constructed in this way is to be seen in that wire pellets or other solids cannot remain adhering to the rod. Thus, due to the rotation of the screening device and because of the turn of the rod, the wire pellets are thereby pushed down in the conveying direction. Blockages are therefore effectively avoided.
In accordance with another feature of the invention, the rod is constructed as a spiral with a plurality of turns, in particular with about four to ten turns.
In a screening device of this kind, which may also be referred to as a xe2x80x9cspiral screenxe2x80x9d, the solids to be screened are introduced into the interior formed by the three-dimensional spiral. Fine solids having smaller dimensions than the distance between two turns of the spiral fall through the spiral, while coarse solids are conveyed further in the interior. The maximum size of the screened finer solid constituent can be set by a suitable choice of the distances between the turns. The rotational movement of the spiral ensures that the coarser solid fragments are transported reliably and continuously in the conveying direction from the start to the end of the spiral.
An essential advantage of the spiral is that waste fragments possibly jammed between two turns are raised as a result of the rotational movement and, in particular, fall down due to their dead weight at an upper reversal point. The simple and robust construction of the screening device as a spiral therefore automatically avoids permanent blockages and allows continuous operation.
In accordance with a further feature of the invention, a number of rods are provided and the rod starts thereof are disposed so as to be offset in terms of rotation. In this case, each rod runs along a helical line. Such a screen having a plurality of rods is also referred to as a multi-flight screen.
In accordance with an added or alternative feature of the invention, the angle of rotation of the rods is smaller than 360xc2x0. In particular, the angle of rotation is smaller than or approximately equal to 180xc2x0. The screening device may be constructed with a plurality of rods which do not execute a complete revolution, so that it can be made more robust, as compared with a spiral screen having a plurality of turns.
In accordance with an additional feature of the invention, there is provided a rod element fixed relative to the rod, both in the spiral screen and in the multi-flight screen. The rod element runs essentially parallel to the outer surface formed by the spiral or parallel to the outer surface formed by the multi-flight screen.
This rod element acts as follows as a stripping element: when a wire pellet catches on the rod, then, as a result of the rotational movement of the screen, this wire pellet is guided against the fixed rod element and is stripped off from the rod by the fixed rod element along the helical line. In order to achieve this, the direction of rotation of the rod is suitably coordinated with the direction of rotation of the screening device.
In accordance with yet another feature of the invention, in order to provide stripping which is as efficient as possible, the rod element is likewise wound along a helical line, specifically and in particular in opposition to the rod, so that, for example, the rod element forms an angle of preferably 90xc2x0 with the rod.
In accordance with yet a further feature of the invention, the spiral is fastened in the spiral screen only at one of its two ends, so that the spiral axis is curved downwards in the direction of gravity towards its non-fastened end as a result of dead weight. Preferably, the spiral is held only at the spiral start, while the spiral end which is located in the conveying direction is constructed to be freely suspended.
As an alternative to a spiral fastened on one side, an already curved spiral may also be fastened on both sides. It is essential that the spiral be curved.
The decisive advantage of the curvature is to be seen in that the distances between the turns on the underside of the spiral are smaller than the distances on the top side of the spiral. Solids introduced into the spiral may, in principle, be jammed only between turns on the underside of the spiral, since the solids fall downwards due to their dead weight, as soon as they are raised. In other words: due to the spiral movement, a jammed solid fragment is raised upwards along with the spiral. At the same time, the distance between the turns widens, so that the solid fragment cannot remain jammed between the turns and necessarily falls down due to its dead weight. The screening device with a curved spiral is therefore to a great extent self-cleaning.
In accordance with yet an added feature of the invention, in order to make the curvature of the spiral possible, it is expedient for the spiral to have a flexible construction. At the same time, stresses acting on the spiral due to jammed solid fragments are thereby kept low.
In accordance with yet an additional feature of the invention, in order to provide a stable and simple construction, the rod forming the spiral is advantageously metallic and, in particular, a round iron bar or an iron or steel tube. Such a spiral is extremely robust and is also suitable, in particular, for the coarse separation of heavy and large solids. The spiral is made from plastic, for example, for instances of use in which only slight loads occur.
In accordance with again another feature of the invention, there is provided an aligning device for the alignment of elongate solid fragments in the conveying direction in the screening device. The aligning device is disposed upstream of the rod in the conveying direction and opens into the interior.
The alignment of elongate solid fragments ensures that they are introduced, essentially parallel to the longitudinal axis, into the interior. Elongate solid fragments are therefore likewise treated automatically as coarse solid fragments and conveyed further. They cannot fall through the spiral perpendicularly to the longitudinal axis. This ensures that the solid fragments falling through the screen formed by the rod or rods are only those which have their largest dimensions being smaller than the distance between two turns of the spiral or the distance between two rods.
In accordance with again a further feature of the invention, the aligning device is constructed as a drum rotatable about its longitudinal axis in order to ensure simple alignment of the elongate solid fragments. The solid fragments are automatically aligned in the direction of the drum axis by virtue of the rotational movement of the drum.
In accordance with again an added feature of the invention, there is provided a coil, that is to say a helically wound strip, placed on the inside of the drum. This coil prevents solids, introduced into one drum end, for example through a filler shaft, from running through the drum at too high a speed, so that the solids xe2x80x9cflyxe2x80x9d through the interior formed by the rod, without screening taking place. Preferably, the coil has a multi-flight construction for this purpose, that is to say a plurality of helical strips, which are disposed so as to be offset in terms of rotation. The coil is, in particular, disposed directly on the inlet side of the drum and has a relatively high side.
In accordance with again an additional feature of the invention, the coil is constructed in such a way that it forms a closed circle, as seen in a top view in the direction of the longitudinal axis of the drum.
This rules out the possibility of solids on the drum bottom being able to slide through, unobstructed, in a straight line from the drum entrance as far as the drum exit. A multi-flight coil with an angle of rotation smaller than 360xc2x0 is preferred so as not to impede the solid flow unnecessarily. In this case, the desired overlap of the side is achieved and, at the same time, a relatively low pitch of the coil is made possible, so that it becomes possible for solids to be transported quickly within the drum.
In an alternative embodiment, the aligning device is constructed as a profiled vibrating bottom which is provided with longitudinal grooves running in the conveying direction and in which the elongate solid fragments are aligned in these longitudinal grooves due to the vibrations of the vibrating bottom.
In accordance with still another feature of the invention, the rod is fastened to the drum on the end surface of the drum located in the conveying direction and, in particular, is welded there. The rod is preferably fastened in such a way that the drum exit opens into the interior formed by the rod. Therefore, in order to provide a frictionless material discharge from the drum, the rod is fastened to the outer wall of the drum or is at least flush with the drum.
In this embodiment, the aligning device and the rod form a structural unit with a particularly simple construction which is robust and reliable.
In accordance with still a further feature of the invention, the screening device is connected to a discharge side of a low-temperature carbonization drum of a pyrolysis plant for the screening of pyrolysis residues obtained from the low-temperature carbonization drum.
In the pyrolysis plant, a first separation of the pyrolysis residue into a fine and a coarse residue fraction is preferably carried out through the use of the screening device. Reliable and continuous operation of the entire pyrolysis plant is ensured by virtue of the simple and particularly robust construction of the screening device.
It is particularly advantageous and expedient for the screening device to be fixedly connected directly to the low-temperature carbonization drum on the discharge side of the latter. Consequently, no other components, which may cause a fault, are interposed between the low-temperature carbonization drum and the screening device. The rod is, for example, fastened directly to a discharge pipe of the low-temperature carbonization drum and is disposed within a discharge device. This discharge device is preferably sealed off in a gas-tight manner relative to the outside atmosphere, in order to avoid the ingress of atmospheric oxygen which would lead to combustion of the combustible and hot pyrolysis residue.
In accordance with still an added feature of the invention, particularly for the purpose of the coarse screening of residue from a large-scale pyrolysis plant, the distance between two turns of the spiral or between two rods is advantageously about 100 mm to 300 mm and, in particular, about 180 mm.
In accordance with still an additional feature of the invention, the interior formed by the rod has a length of about 0.5 to 1.5 m. Its diameter amounts to about 1.5 m, and a screening device with a drum and a screen preferably has a total length of about 2 to 4 m. The length of the interior is expediently smaller than or equal to the diameter of the drum.
With the objects of the invention in view, there is also provided a method for screening solid residues from a pyrolysis plant for refuse, which comprises providing a screening device having a longitudinal axis, an interior and a rod wound along a helical line; introducing residues into the interior of the screening device rotating about the longitudinal axis; and conveying coarse residue constituents with the rod for separating the coarse residue constituents from pure residue constituents.
In accordance with a concomitant mode of the invention, there is provided a method which comprises initially aligning the residues in a conveying direction in an aligning device and subsequently screening the residues with the rod.
The advantages and particular embodiments explained with reference to the screening device also apply accordingly to the method.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a pyrolysis plant for refuse and a method for screening solid residues, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.